The invention relates to a method of manufacturing an assembly of conductors, wherein a void is provided in an electroconductive plate, within which an island is formed which serves as a carrier for a semiconductor element, and which is connected to the assembly by a part of the plate, a number of strip-shaped conductors being formed within the void, which are situated around the island, and the void being formed such that one of the strip-shaped conductors is connected to the island by means of a further part of the plate. The invention also relates to a semiconductor device manufactured by means of such an assembly.
By virtue thereof, a connection region situated on the upper side of the semiconductor element can be readily connected to the lower side of the semiconductor element, namely by means of a wire connection between the upper side of the semiconductor element and the conductor. Such a connection is important for various semiconductor elements, such as in particular high-frequency ICs wherein the uppermost part, generally an epitaxial layer, is separated from the lowermost part, generally the substrate, by means of a high-impedance intermediate layer. In addition, or instead, such a conductor connected to the island may provide for an improved heat dissipation from the island, thus rendering the assembly extremely suitable for semiconductor elements which, in operation, dissipate relatively much heat.
Such a method is known from European patent specification 0.102.988, published on Sep. 21, 1988. In said document, FIG. 3 shows how an assembly of conductors is formed in a metal plate by means of a void wherein an island is formed which is surrounded by a number of conductors facing said island. The island is connected to the assembly by means of two parts of the plate. One of the conductors adjoining one of said parts is connected to said part of the plate by means of a further part of the plate. This conductor then demonstrates the above-mentioned advantages.
A drawback of the known method resides in that the assembly obtained by means of said method is relatively expensive. This drawback relates in particular to a number of ICs for consumer applications, such as ICs for use in mobile telephony and audio equipment. These ICs often are customized ICs, which are ordered for a relatively short period of time and thus are manufactured in relatively small numbers.
Therefore, it is an object of the invention to provide a method which enables an assembly of conductors to be obtained in a simple and inexpensive manner, in particular, when said assembly of conductors is to be used in said ICs for consumer applications.
To achieve this, a method in accordance with the invention is characterized in that the void is formed in such a manner that two or more strip-shaped conductors are electroconductively connected to the island by means of a further part of the plate, and at least one of the further parts of the plate is removed by means of punching. The invention is first of all based on the recognition that the known assembly can only suitably be used for a limited number of ICs because the desired position of the conductor connected to the island is not always the same. The invention is further based on the recognition that if an assembly is manufactured by means of photolithography and etching, which is most likely, then the assembly can be readily adapted but is still relatively expensive. The invention is finally based on the recognition that the use of the punching technique to manufacture the assembly is expensive, particularly, because each different IC requires the manufacture of a completely new punching tool. This is not only expensive but also time-consuming. By forming a conductor at various locations in the assembly, connecting said conductor to the island and, subsequently, removing the conductor at locations where it is not necessary by means of punching, important economies can be achieved: large numbers of semi-manufactured products of an assembly can be manufactured using one and the same punching tool. To obtain an assembly which can suitably be used for the intended semiconductor element, a number of connections between the island and the conductors are interrupted, namely those connections which are unnecessary or undesirable for the IC for which the assembly is intended. Said interruption can be readily carried out by means of punching using relatively simple punching tools. In accordance with the invention, only the latter punching tools have to be adapted to the intended application. As a result thereof, the method in accordance with the invention is both inexpensive and fast. That is to say, when the intended application changes, the production of an intended assembly can be started very rapidly.
In an important embodiment of a method in accordance with the invention, one or more of the conductors situated next to the part of the plate via which the island is connected to the assembly, are connected to the part of the plate by means of a first further part of the plate. In this manner, for each part of the plate to be connected to the island, two conductors can be connected to the island. In practice, the island often is connected to the assembly by means of two, or even four, parts of the plate. In these cases, maximally four or eight conductors can be connected to the island. If the number of (initially) chosen connections is N, and the number of removed connections is M, where M is smaller than or equal to Nxe2x88x921, then it applies that the removal of said M connections can take place in (N over M)-ways. That is to say, in N!/(M!*(Nxe2x88x92M)!) ways. This variant is particularly suitable for making an electrical interconnection between the substrate and the island and hence for the above-mentioned very fast ICs for use, for example, in mobile telephony applications. An important advantage of this variant is that relatively little (mechanical) stress develops in the semiconductor device to be manufactured, so that this semiconductor device and, in particular, the electrical interconnection is very reliable.
In a preferred embodiment of a method in accordance with the invention, one or more of the conductors are directly connected to the island by means of a second, further part. This variant has the important advantage that also conductors which are not situated next to a part of the plate connecting the island to the assembly can be connected to the island. In this manner, in fact, all conductors can be connected to the island. This results in the freedom of manufacturing an assembly which can suitably be used for any IC. Also in this case, the minimum number of connections that is removed again by punching is 1. It is noted that this manner of making (temporary) connections between a conductor and the island can also be used for a conductor which does border on a part of the plate connecting the island to the assembly. This variant is particularly suitable for optimally cooling the island and hence for use in medium-power ICs, for example for the above-mentioned audio application.
Preferably, also for forming the void, use is made of the punching technique. The void does not necessarily have to be formed in a single (punching) step. In fact, it is preferred to form the void in a number of (punching) steps so as to enable a uniform removal and preclude the development of stresses in the assembly.
In a very important variant, the void is formed such that it demonstrates a prolongation into the island on either side of a conductor. By virtue thereof, the further parts to be removed again, particularly those further parts which form a direct connection between the island and a conductor, can very readily be removed by punching. A relevant aspect in this connection is that the further parts which have been removed again by punching are preferably removed by means of a C-shaped punch which contains a void at the location of a further part to be saved. As a result, only this punch has to be adapted to the intended IC to manufacture the suitable assembly. This can be carried out rapidly as well as inexpensively, so that this variant is very attractive.
After the assembly has been given a suitable structure for the intended IC, the relevant IC (semiconductor element) is mounted on the island and electroconductively connected to the different conductors, for example by means of wire connections, whereafter the IC (semiconductor element) thus provided with conductors is provided with a protective envelope and, finally, an individual semiconductor device is obtained by removing the semiconductor element provided with the envelope and the conductors from the assembly. As noted hereinabove, a medium-power and/or high-frequency IC is preferably chosen for the semiconductor element. The invention also relates to a semiconductor device obtained by means of a method in accordance with the invention.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.